An apparatus consistent with the present invention relates to a sunroof panel apparatus for a vehicle which is able to illuminate its cabin.
There are different types of lights used in the cabin of a vehicle, such as a room light for uniform illumination, a personal light for reading by a passenger without disturbing the view of a driver and a map light for reading a map. It has been worked out to select an appropriate one according to purposes. For example, Japanese Examined Utility Model Application Publication S56-1465 discloses a lighting apparatus for illuminating a cabin of vehicle which is an integrated assembly including a room light and a personal light, thereby decreasing the number of parts.
However, the conventional lighting apparatus disclosed in the above document creates such a high contrast between an illuminated portion and a shadowed portion that it contributes to eyestrain. In addition, it spoils the beauty of the cabin, because the lighting apparatus dictates that its unit including a lamp and a lens protrudes from the ceiling of cabin.
On the other hand, an electro-luminescent (EL) sheet has been widely noticed of late years as lighting and display apparatus, which excels in achieving thinner thickness, lighter weight as well as more luminescent colors. FIG. 6 is an example of cross sectional view illustrating the structure of EL sheet. As shown in FIG. 6, an EL sheet 60 includes a transparent base plate 61. A transparent electrode layer 62 is formed on an upper surface of the transparent base plate 61. A luminous layer 63, an insulation layer 64 and a back electrode layer 65 are one by one laid down on the transparent electrode layer 62. Incidentally in FIG. 6, thickness of a layer relative to the total thickness of whole layers is schematically illustrated with an unrepresentative dimension, for convenience sake. Hereinafter, drawings illustrating the structure of an EL sheet are described in a similar fashion.
When the EL sheet 60 is connected to an AC power supply 66 so as to impose an alternate voltage on it, it emits light by repeating separation and recombination of electrons and positive holes in the luminous layer 63. In this connection, a material which possesses a smaller work function relative to the transparent electrode layer 62 is required for the back electrode layer 65. However, practically speaking, it is difficult to find a material which meets both the small work function and transparency. This results in use of an opaque material for the back electrode layer 65. In this case, the EL sheet 60 shown in FIG. 6 emits light through the transparent base plate 61 (downward direction in FIG. 6)
A panel including laminated sheets of glass, between which the EL sheet 60 is enclosed, can be used as a sunroof panel apparatus with illumination for a vehicle (hereinafter referred to as “sunroof panel apparatus 72”), if it is mounted to a vehicle in the following manner. As shown in FIG. 7, this apparatus 72 is installed in an opening 71 made in a fixed vehicle roof 70 while the transparent base plate 61 is oriented toward the inside of a cabin. FIG. 8 is a schematic diagram illustrating a sectional structure of the sunroof panel apparatus 72 which encloses the EL sheet 60. As shown in FIG. 8, the EL sheet 60 (layer structure not shown) is sandwiched between laminated sheets of glass 74a and 74b through transparent enclosing members 73a and 73b. Because the EL sheet 60 uniformly emits light by surface luminescence, the sunroof panel apparatus 72 can prevent eyestrain. Furthermore, because the EL sheet 60 is enclosed between the laminated sheets of glass 74a and 74b and free from protrusions, the sunroof panel apparatus 72 does not spoil the beauty of the cabin of a vehicle.
However, the sunroof panel apparatus 72 is not satisfactory when it is used as a light illuminating the cabin for multiple purposes described above. The luminescence created by the EL sheet 60 can serve as a room light, but can not serve as a personal light or a map light which requires locally high illumination.